Audisto Canonical Checker

How to detect canonical issues

The Audisto Crawler identifies common mistakes in canonical usage. Use this group of reports to keep your canonical definitions valid.

Wrong usage of canonical links can cause issues with duplicate content, when content is available on more than one URL.

Example: Audisto Canonical Check with the canonical hint reports for the current crawl

Audisto Canonical Check with the canonical hint reports for the current crawl

It is crucial to have valid canonical definitions, because otherwise a multitude of duplicate content related issues is likely to harm the search engine rankings of your site.

For further information read our rel=canonical guide.

Here is a list of all specific hints related to usage of rel=canonical on your website, that can be identified with the help of the Audisto Crawler.

Table Of Content

Hints

<link rel="canonical"> URL is not absolute

Description

If the canonical element specifies a URL relative to the document's URL, document's URL is flagged with this hint.

This report shows all occurrences of canonical usage with URLs that are not absolute.

Examples

Absolute URL

<link rel="canonical" href="http://example.com/folder/page.html">

Short URL

<link rel="canonical" href="page.html">

Short URL - root folder relative

<link rel="canonical" href="/folder/page.html">

Short URL - protocol relative

<link rel="canonical" href="//example.com/folder/page.html">
Importance

Using shortened URLs for canonical links can lead to several kinds of duplicate content issues:

  • duplicate content issues with different protocol versions
  • duplicate content issues with different domains
  • duplicate content issues with different folders
Operating Instruction

We suggest using absolute URLs for canonical links.

<link rel="canonical"> contains malformed or empty href

Description

This hint identifies all occurrences of canonical elements that contain an empty or invalid target URL.

Examples

Empty canonical

<link rel="canonical" href="">

Malformed canonical

<link rel="canonical" href="htp://example.com/">
Importance

Malformed or empty href in canonical links cause canonical definitions to be invalid and can cause issues with duplicate content when a document is available on more than one URL.

Operating Instruction

We suggest to check for malformed or empty canonical href on a regular base.

<link rel="canonical"> found

Description

A canonical-element has been found, either as a <link> tag with rel="canonical" or an according link header.

Examples

Canonical in HTML <head>

<link rel="canonical" href="http://example.com">

Canonical in HTTP header

HTTP/1.1 200 OK
Content-Type: application/pdf
Link: <http://example.com/page.html>; rel="canonical"
Content-Length: 4223
...
Importance

Canonical links are a valuable tool for webmasters to define the preferred version of a document if it is available on more than one URL at the same time.

Operating Instruction

Use the “canonical found" hint report to identify all URLs that contain a canonical link definition and find out how many URLs on the crawled site have canonical link definitions.

<link rel="canonical"> found outside <head>

Description

A canonical element was placed outside of the <head> section, search engines will ignore it.

This report helps you to identify all occurrences of canonical definitions, that are invalid due to being placed outside the <head> tag on the crawled website.

Example
<html>
  <head>
    ...
  </head>
  <body>
    ...
    <link rel="canonical" href="http://example.com/">
    ...
  </body>
</html>
Importance

Some search engines ignore improper canonical designation. If canonical definitions get ignored by search engines, this might cause issues with duplicate content and representation of the site in search results.

Operating Instruction

Keep your canonical definitions inside the HTML <head> tag, so they don't get ignored by search engines.

<link rel="canonical"> found twice

Description

More than one canonical elements was found, either as a <link> tag with rel="canonical" or an according link header.

This report shows all URLs with double canonical definitions on your website, that we were able to identify.

Examples

HTML Head

<link rel="canonical" href="http://example.com/">
<link rel="canonical" href="http://example.com/">

HTTP Header

Link: <http://example.com/>; rel="canonical"
Link: <http://example.com/>; rel="canonical"

HTML Head & HTTP Header

<link rel="canonical" href="http://example.com/">

Link: <http://example.com/>; rel="canonical"
Importance

Using more than one canonical link element can cause conflicting definitions or unexpected behaviour when documents are available on more than one URL at a time.

Operating Instruction

We suggest identifying all URLs that have more than one canonical link element defined. We also suggest looking for the reason behind the double definition, as this problem usually can be traced back to third party code (plugins, extensions and add-ons of the CMS).

If canonical definitions are found twice on a document, this often occurs due to usage of multiple SEO plugins or a SEO plugin in combination with manual canonical definitions.

<link rel="canonical"> found twice and differs

Description

More than one canonical elements have been found, either as a <link> tag with rel="canonical" or an according Link header. Additionally, they specify different targets.

This report allow you to identify all occurrences of double canonical definitions with conflicting target URLs.

Examples

HTML Head

<link rel="canonical" href="http://example.com/">
<link rel="canonical" href="http://example.com/page1.html">

HTTP Header

Link: <http://example.com/>; rel="canonical"
Link: <http://example.com/page1.html>; rel="canonical"

HTML Head & HTTP Header

<link rel="canonical" href="http://example.com/">

Link: <http://example.com/page1.html>; rel="canonical"
Importance

Having more than one canonical link element with different target URLs in a document can cause search engines to ignore the canonical definitions. This might lead to issues with duplicate content.

Operating Instruction

We suggest correcting all conflicting canonical definitions by removing the unnecessary definition.

<link rel="canonical"> not found

Description

A canonical-element has not been found, neither a <link> tag with rel="canonical" nor an according link header. This may be intended.

This report identifies all URLs on the crawled website, that do not have a canonical link element.

Importance

Missing canonical definitions can lead to issues with duplicate content if the document is a duplicate of another document on the site. This can also happen if 3rd party sites copy your content or you syndicate your content.

Operating Instruction

We suggest using canonical definitions in any case. Canonical links should be self referencing by default.

<link rel="canonical"> points to other URL

Description

If the canonical element is found and points to a different URL, the URL is flagged with this hint.

Use this report to identify all instances of canonical elements pointing to other URLs.

Examples

The canonical link element points to the SSL version of the document:

Canonical link element for http://example.com/page.html

<link rel="canonical" href="https://example.com/page.html">

The canonical link element points to a URL without GET-parameter:

Canonical link element for http://example.com/page.html?a=1

<link rel="canonical" href="http://example.com/page.html">
Importance

The canonical link URL specifies a prefered version of a document that is available on more than one URL at a time.

By using a canonical link element pointing to another URL, you are telling search engines to prefer the target URL in search results.

If URLs that are not supposed to be shown in search results are part of the internal link graph, this can lead to waste of crawl budget.

Operating Instruction

You might consider changing internal links to point directly to the prefered version of the document to save crawl budget.

You might also want to evaluate if multiple URLs for one document are necessary at all.

<link rel="canonical"> points to same URL

Description

If the canonical element is found and points to the same URL, the URL is flagged with this hint.

This report shows all occurrences of self referencing canonical link elements on the crawled website.

Example

Canonical link element for http://example.com/page.html

<link rel="canonical" href="http://example.com/page.html">
Importance

Self referencing canonical is the suggested way to use canonical definitions. It prevents duplicate content issues if 3rd parties copy or syndicate your content.

Operating Instruction

You might want to remove the canonical element from the HTML to decrease file size. However this might lead to problems when 3rd parties copy or syndicate your content.